1. Field of the Invention
The present invention relates to a process and a system for monitoring a paper machine""s drainage element, which includes at least one ceramic.
2. Description of the Related Art
A suction box used in a system for monitoring a paper machine""s drainage element is known, for example, from German patent specification DE-PS 233 618 and European patent registration EP 0 831 173 A2 (PB10359 EP).
Not enough rinse water during the start up phase of the machine for manufacturing a fibrous web (especially a paper, cardboard, or tissue web) from a fibrous suspension can lead to overheating of the drainage elements. The resulting thermal load can be particularly damaging when thermal tensions arise in the ceramic, which could lead to a fracture in the ceramic, or when glued points between the ceramic and the main body soften, thereby creating the danger that the ceramic may slide or detach.
In general, there are two different possibilities that could lead to failure of a ceramic:
1. The adhesive remains stable and the ceramic breaks due to the direct thermal load on the ceramic.
2. The ceramic itself would withstand the thermal load, but the adhesive becomes soft and the small individual ceramic plate protrudes in one area progressively into the wire. This leads to a greater thermal load, resulting in fracture.
Of course, a combination of both cases may also occur. For case 1, the temperature is measured close to the surface of the ceramic; for case 2, the temperature is measured on the adhesive point. Due to the constantly increasing machine speeds, even a short period of insufficient cooling, which can never be ruled out under practical operational conditions, could lead to destruction of the ceramic.
Although the article xe2x80x9cAuswahlkriterien fxc3xcr Keramik-Belxc3xa4ge in schnelllaufenden Papiermaschinen unter Berxc3xcicksichtigung ihres Einflusses auf die Konstanz der Siebpartiexe2x80x9d, written by K. D. Fuchs and published in, among other publications, Wochenblatt fxc3xcr Papierfabrikation 23/24, 2000, (pages 1631-1635, especially page 1633, left column) mentions simulation experiments with which thermal elements are used to measure the temperature on the lining surfaces in the wet section (sheet formation unit) and in the press section, the article deals primarily with the criteria for selecting ceramic coatings. Moreover, apparently temperature was measured only on the surface of the ceramic.
A machine for manufacturing a fibrous web, and, more particularly, a paper, cardboard, or tissue web, from a fibrous suspension, with a sheet forming area in which the developing fibrous web is led by way of at least one porous fabric, especially a mesh screen, over at least one suction box that has a main box that has at least one connection, including a line, to at least one vacuum source. The at least one suction box also has at least one suction box covering that is formed by at least two drainage elements, especially drainage rails, that run laterally to the machine""s running direction, border a suction slit, and each of which has one main body and at least one ceramic, whereby preferably each of the at least one suction slits in both edge zones of the fabric is bordered by a format slide that has a main body and at least one ceramic. The term sheet-forming unit includes both a former, for example, a twin-wire former or a hybrid former, as well as a wire section, especially a Fourdrinier wire part.
The present invention provides an improved machine for manufacturing a fibrous web from a fibrous suspension with which is ensured economical and reliable monitoring of the affected drainage elements and with which possible damage is avoided. An advantage of the invention is simple and economical subsequent installation and exchange of temperature sensors on existing drainage elements.
According to the present invention, a machine for manufacturing a fibrous web from a fibrous suspension accomplishes this task with at least one drainage element and/or format slide that exhibits a removable edge piece inside which at least one temperature sensor is integrated.
These temperature sensors can be used to measure the temperature in the ceramic and/or the temperature at an adhesive point between the ceramic and the related main body and/or the temperature in the main body, thereby ensuring economical and reliable monitoring of the affected drainage elements and avoidance of potential damages.
The removable edge piece also creates the ideal condition both for simple and economical subsequent installation of a temperature measurement system as well as rapid and economical exchange of temperature sensors on existing drainage elements.
There are two primary preferred temperature measurement positions. In the first form, the temperature sensor is placed in the ceramic close to the ceramic surface, where the maximum temperature appears, and on any desired position above the section of the width of the drainage element that is wetted by the fabric. The maximum temperature usually appears on edges, where the fabric contacts it or runs off. For this reason, temperature measurement without mechanical contact with the so-called xe2x80x9chotxe2x80x9d spot (using infrared for example) is not practical. For this reason, a second promising form involves arranging the temperature sensor in a recess in the ceramic. The recess in the ceramic is normally created before sintering (when the ceramic is still green). The advantage of this method of production is that it does not contribute to internal stresses in the ceramic or in the area around the recess or opening. The recess can be created especially during a molding process.
A temperature measurement is generally practical in the machine""s direction of operation only at the following locations:
a) at the beginning and end of a drainage element, for example, at the first and last drainage rails of a suction box,
b) especially where there is a high vacuum and/or a fabric guide with a rail or a lining,
c) in general anywhere there is a high specific pressure of the fabric on the ceramic and/or
d) where there is insufficient lubrication caused by low drainage or the absence of spray water.
Accordingly, a temperature sensor is planned for at least one of the mentioned locations, as needed.
It is also advantageous when several temperature sensors are arranged laterally to the machine""s running direction at an appropriate distance from each other. The distance between the measurement points can be approximately 500 mm, for example. Thermocouples are the preferred temperature sensor type because they have historically demonstrated satisfactory price/performance, operational safety and maintenance characteristics.
The preferred material for the main body of the drainage element is glass fiber-reinforced plastic. This type of material has proven its value in the paper industry.
From the perspective of costs and process technology, the ceramic of the drainage element and/or the format slide is shaped like a small ceramic plate and has a height of 1 mm to 10 mm, preferably from 2 mm to 6 mm.
The format slide can be slid laterally relative to the machine""s running direction in order to facilitate simple adjustment of the width of an individual suction zone and thereby the suction box""s individual suction surface.
The format slide includes either one part or several parts, each preferably with a constant height. Both variations of the format slide can be equipped with at least one height adjustment mechanism, whereby the preferred design of the height adjustment mechanism consists of at least one adjustment screw together with the accompanying locking screw.
In another embodiment, height adjustment can be accomplished through mutual sliding of the format slide with the drainage element. In order to avoid or reduce by the greatest degree possible damage and/or wear to the fabric running over the drainage element, the format slide has an extension that extends in the direction of the middle of the machine and preferably comes into contact with the fabric. In addition, the extension should be permeable for a fluid such as air or water.
When viewed from above, the extension is wedge-shaped and/or perforated to increase permeability for the fluid. The format slide can also exhibit a surface profile in contact with the fabric that is very similar to that of the drainage element.
According to a second aspect, the present invention is based on the task of providing an improved process and an improved system, as described previously, with which is ensured economical and reliable monitoring of the affected drainage elements and with which possible damages are avoided.
According to the present invention, this second task is accomplished with a process for monitoring a paper machine""s drainage element, which includes at least one ceramic, with the following process steps:
a) the temperature is measured in the ceramic, and/or on one adhesive point between the ceramic and a related main body, and/or in the main body,
b) the obtained temperature measurement value is analyzed in a process control system related to the paper machine and is preferably compared with at least one selectable threshold value,
c) depending on the result of the analysis or when the selectable threshold value is exceeded, the process control system automatically activates or influences as appropriate at least one control element in order to indicate that the threshold value has been exceeded and/or to initiate at least one appropriate countermeasure that will counteract further heating of the monitored area and/or cool the monitored area.
This design not only ensures automatic monitoring of the affected drainage element but also ensures that countermeasures will be automatically initiated by a process control system upon reaching a critical temperature, for example, in order to prevent further generation of heat and therefore possible damage. In other words, process steps will be automatically initiated as necessary in order to affect, for example, slow cooling of the ceramic material.
In addition, the design takes into account the fact that, with respect to thermal loads, there are in principle two critical locations on the ceramic, namely the adhesive point and the area of the ceramic close to the surface.
Considering the adhesive, the adhesive""s softening point is lower than the temperatures that could lead to failure of the ceramic due to thermal stresses. Therefore, it is advantageous to monitor the temperature at the adhesive point. If the adhesive softens, the positions of the individual ceramic plates may become unstable. As a result, the pieces may fall further into the wire and thereby be subjected to higher thermal stresses, which could lead to failure. Furthermore, a change to the plate""s location could cause increased wear to the wire and have negative effects on the formation of the paper or cardboard. The process according to the present invention can counteract this.
According to a preferred design of the process according to the present invention, temperature measurement is part of a control system that also includes signal conversion, which follows the measurement of temperature, as well as data processing performed by way of the process control system.
Regarding the ceramic surface, the temperature in the ceramic should be measured close to the surface of the ceramic, where the maximum temperature occurs.
The maximum temperature usually appears at edges where the wire contacts it or runs off. For this reason, temperature measurement without mechanical contact with the so-called xe2x80x9chotxe2x80x9d spot (using infrared for example) is not practical. According to practical design of the process according to the present invention, a recess is created in the ceramic, a temperature sensor is placed into the recess, and the temperature in the ceramic is measured by the temperature sensor in the recess. The recess in the ceramic is normally created before sintering (when the ceramic is still green). The advantage of this method of production according to the present invention is that it does not contribute to internal stresses in the ceramic or in the area around the recess or opening. The recess can be created especially during a molding process. Although the recess should be created when the ceramic is in the green state (before sintering), it is also possible to work the recess into the ceramic after the ceramic has been sintered.
It is advantageous for at least one of the following countermeasures to be initiated if a respective threshold value is exceeded:
a) reduction of the speed of the mesh screen, preferably to standstill;
b) particularly slow increase of the rinse water volume;
c) reduction of the vacuum on the drainage element.
To do so, at least one of the following steps, for example, can be initiated. At least one spray tube, for example, can be appropriately influenced in order to change the spray water flow rate. To change the speed of the paper machine, at least one of the paper machine""s drives can be appropriately influenced. To reduce the vacuum on the drainage element, at least one valve can be appropriately adjusted. In addition, it is also possible, for example, to reduce the wire tension by appropriately adjusting at least one tension roller. If a threshold value is exceeded, an alarm signal, for example, can also be generated. It is advantageous if the alarm signals when the measured temperature exceeds approximately between 80xc2x0 C. and 120xc2x0 C. or when the rate of temperature increase is greater than 2xc2x0 C. per second. The previously mentioned control elements can be, for example, spray tubes, paper machine drives, valves, tension rollers, signal emitters, and/or similar devices.
According to a functional design of the process according to the present invention, first a warning signal is generated when an initial threshold value is exceeded and, when another threshold value is exceeded, at least one corresponding countermeasure is initiated with which further warming of the monitored area is counteracted and/or the monitored area is cooled.
A temperature measurement is generally practical in the machine""s direction of operation only at the following locations:
a) at the beginning and end of a drainage element, for example, at the first and last ceramic rail of a flat suction box;
b) especially where there is a high vacuum and/or a wire guide with a rail or lining;
c) in general, wherever the wire exhibits a specific high pressure on the ceramic and/or
d) where there is insufficient lubrication caused by low drainage or the absence of spray water.
Accordingly, a thermal sensor is planned for at least one of the mentioned locations, as needed.
It is also advantageous if the temperature is measured, viewed laterally to the machine""s running direction, at several points separated from each other by an appropriate distance. Accordingly, the distance between the measurement points can be approximately 500 mm, for example.
A thermocouple is the preferred temperature sensor.
The monitoring system according to the invention includes as appropriate at least one temperature sensor, connected to a process control system assigned to the paper machine, in order to measure the temperature in the ceramic and/or the temperature at an adhesive point between the ceramic and an assigned main body and/or the temperature in the main body, whereby the obtained temperature measurement value is analyzed in the process control system and preferably compared with at least one selectable threshold value. Depending on the result of the analysis or when the selectable threshold value is exceeded, the process control system can automatically appropriately activate or influence a control element in order to signal that the threshold value has been exceeded and/or initiate at least one appropriate countermeasure with which further warming of the monitored area is counteracted and/or the monitored area will be cooled.
It is clear that the invention""s previously described characteristics and the characteristics to be described in the following can be used not only in the indicated combination, but also in other combinations or individually without leaving the framework of the present invention.